Hydraulic fan drive systems for buses and the like have traditionally required a dedicated flow source to allow sufficiently accurate control of fan speed. This requires either a dedicated fan drive pump, or a dedicated flow amount from a priority flow source from a pump. It is desirable, however, in some applications, to use only a portion of the total flow from an existing hydraulic pump, and share the total pump flow with other work functions on the machine.
It is therefore a principal object of this invention to provide a speed modulating hydraulic fan drive system which shares flow from one source with other work functions.
A further object of this invention is to provide a speed modulating hydraulic fan drive system which will reduce the number of pumps required for the total work system.
A still further object of this invention is to provide a speed modulating hydraulic fan drive system which utilizes a pressure reducing valve which will allow only enough fluid to pass to develop the desired fan motor pressure drop.
A still further object of this invention is to provide a speed modulating hydraulic fan drive system which makes use of an electronic controller to command the pressure level of the pressure reducing valve, and which can respond directly to a communication signal of the electronic controller of the engine of the vehicle.
These and other objects will be apparent to those skilled in the art.